Background: We have discovered a defect in the cellulose acetate filter used on many popular brands of cigarettes which may pose a health risk to smokers. Tiny fragments of cellulose acetate are released from the filter. Our studies show that the fibers, coated with tobacco tar, are likely to be ingested and inhaled by smokers. There is ample evidence to suspect that cigarette fibers remain in the lungs for years and, in combination with their adsorbed tar may contribute to malignant transformation and other lung illnesses. It is also conceivable that a filter design could be modified to correct the fiber shedding defect. Objectives: The objectives of this project are to: l) enumerate and compare the fiber shedding characteristics of the top selling cigarette brands; 2) identify features of the cigarette, filter design, and other factors which influence fiber release; 3) define health risks associated with inhaling and/or ingesting filter fibers; and 4) evaluate the cigarette industry's awareness of the fiber shedding defect. Methods: The release of filter fibers will be assessed under different conditions using a series of standardized testing procedures previously developed in our laboratory. Fibers will be identified and enumerated using microscopic and infrared microspectrophotometric procedures. A computerized search of the U.S. patent literature will identify cigarette filter patents which will be used to characterize the key design features of filters on different cigarette brands. Computerized searches of the medical literature will be undertaken to identify studies to define health risks associated with inhaling and/or ingesting filter fibers. Hand searches of the tobacco trade literature, industry reports, and other unpublished data will also be performed. Relevance: Results from this research will provide a scientific basis for regulating the design of cigarette filters. Findings could lead to a ban on the use of cellulose acetate in cigarette filters, a requirement that manufacturers warn consumers about the filter defect, and litigation against filter manufacturers and cigarette companies.